The research field of Nagatsuma laboratory consists of four themes related to the millimeter-and THz-wave frequency range and photonics. These frequencies have been a largely unexplored frequency region until now because the generation and the detection technology in this band is still in its infancy. In our laboratory, we investigate a broad spectrum of topics, beginning with technology for systems interconnect and packaging, to its application to complex systems. Our daily research is intended towards practical realization.
Outline of research themes
Communication Systems Team
In recent years, the development of many wireless communication systems and devices has largely improved the convenience and comfort of our daily live.
However, the increase of the amount of information to transmit and the limited frequency bandwidth are the two main problems of current wireless communication systems. It is therefore necessary to expand the frequency rage used for wireless communication and the speed of data transfer.
We study the application of THz-waves in order to achieve ultra-high-speed wireless communication and focus on three issues : high speed, compactness and sophistication.
We have successfully demonstrated the world’s fastest wireless communication with an error-free data transmission of 48 Gb/s.
- Tadao Nagatsuma, Shogo Horiguchi, Yusuke Minamikata, Yasuyuki Yoshimizu, Shintaro Hisatake, Shigeru Kuwano, Naoto Yoshimoto, Jun Terada, and Hiroyuki Takahashi, "Terahertz wireless communications based on photonics technologies",Optics Express, Vol. 21, Issue 20, pp. 23736-23747 (2013).
- T. Nagatsuma, "Terahertz communications technologies based on photonic and electronic approaches," 18th European Wireless Conference (EW 2012), S13-3 (2012).
- T. Shiode, T. Mukai, M. Kawamura, and T. Nagatsuma,"Giga-bit wireless communication at 300 GHz using resonant tunneling diode detector," Proc. Asia-Pacific Microw. Conf. (APMC2011), pp.1122-1125 (2011).
- "300GHz High-speed wireless communication realized with small device," Tech-On, Nov. 24, 2011.
- "世界初！小型半導体素子(共鳴トンネルダイオード)を 用いてのテラヘルツ帯無線通信に成功," ローム株式会社ニュースリリース, 2011年11月21日．
- T. Nagatsuma, "Extreme bandwidth wireless communications using terahertz waves," 20th International Conference on Applied Electromagnetics and Communications (ICECom 2010), Sept., 2010.
Imaging Systems Team
The term imaging means to visualize objects hidden inside a targeted entity, an envelope for example. THz-waves have the advantage that many materials are transparent to the waves and that compact systems are possible. Compared to X-ray, the energy of THz waves is much lower. Therefore, THz-waves are less taxing on the human body. THz imaging applications are promising for new non-destructive and non-invasive inspection techniques.
Millimeter-waves, which have higher transmittance capability than THz-waves, enable the defect recognition inside objects such as concrete and wooden structure. These imaging applications can solve a lot of issues related to defects in buildings.
The imaging application group in our laboratory studies both the THz- and millimeter-wave frequency range. Utilizing broadband light-sources and interferometer, we have achieved the world’s first successful optical tomography in the THz- and millimeter-wave frequency range. Our goal is to further improve the performance of this application.
- T. Ikeo, T. Isogawa and T. Nagatsuma, "Three dimensional millimeter- and terahertz-wave imaging based on optical coherence tomography," IEICE Transactions on Electronics, vol.E96-C, No.10, pp.1210-1217 (2013).
- T. Isogawa, T. Kumashiro, H.-J. Song, K. Ajito, N. Kukutsu and T. Nagatsuma, "Tomographic imaging using photonically generated low-coherence terahertz noise sources," IEEE. Trans. THz Science and Technology, vol. 2, No. 5, pp.485-492 (2012).
- T. Ikeou, T. Isogawa, K. Ajito, N. Kukutsu and T. Nagatsuma, "Terahertz imaging using swept source optical-coherence-tomography techniques," Proc. Int. Topical Meeting Microw. Photon. (MWP), (2012).
THz-wave Spectroscopy and Measurement Systems Team
Spectroscopy is the study of the interaction between the object under investigation and the energy reflected or transmitted by it when illuminated by a signal source. Using this, information about the object characteristics can be obtained.
Conventional spectroscopy often uses the infrared frequency spectrum, where the object is illuminated by infrared waves. Recently, spectroscopy using signals in the THz-wave region (300 GHz to 3 THz) has attracted a lot of interest.
Every substance has a specific absorption spectrum, called the fingerprint spectrum. In comparison with other electromagnetic regions, the THz region has the advantage of containing the fingerprint spectrums of many substances, especially those of pharmaceutical products, explosives and drugs. Thus, the THz-wave frequency range is potentially extremely effective in substance identification applications.
The THz-wave frequency range is dominated by THz time-domain spectroscopy systems (THz-TDS) using pulsed signals. However, the pulsed laser used in the THz-TDS is not very efficient in terms of size and cost. Our group aims to perform research and to construct a low-cost and convenient system using continuous-wave (CW) signals.
- S. Hisatake and T. Nagatsuma, ''Continuous-wave terahertz field imaging based on photonics-based self-heterodyne electrooptic detection,'' Opt. Lett., vol. 38, No. 13, pp. 2307-2310 (2013).
- S. Hisatake, G. Kitahara, K. Ajito, Y. Fukada, N. Yoshimoto,and T. Nagatsuma, "Phase-sensitive terahertz self-heterodyne system based on photodiode and low-temperature-grown GaAs photoconductor at 1.55 μm," IEEE Sensors Journal, vol. 13, pp. 31-36 (2013).
- S. Hisatake and T. Nagatsuma, "Nonpolarimetric technique for homodyne-type electrooptic field detection," Appl. Phys. Express, vol. 5, 012701(2012).
Systems Interconnect and Packaging Team
In the THz-wave frequency range a variety of applications is expected, which all depend on the technological progress in terms of signal generation and detection.
However, despite their potential, present systems operating in the THz-wave frequency range are quite large and bulky. This is due to the fact that the integration of the individual system components is quite difficult and expensive.
Our group aims to develop integrated systems on the basis of photonic crystal technology. A photonic crystal is an artificial crystal, which has a periodic refractive index distribution in the same order as the electromagnetic wavelength.
We are working towards the realization of compact and planar THz-wave integrated circuits and monolithic integrated circuit components, such as THz-wave absorber using the photonic crystal.
- T. Ishigaki, M. Fujita, M. Nagai, M. Ashida and T. Nagatsuma, "Photonic-crystal slab for terahertz-wave integrated circuits," IEEE Photonics Conference 2012 (IPC2012), pp. 774-775 (2012).
- R. Kakimi, M. Fujita, M. Nagai, M. Ashida and T. Nagatsuma, “Capture of a terahertz wave in a photonic-crystal slab”, Nature Photonics, vol. 8, no. 8, pp. 657-663, 2014.